Process for producing gasoline from a cracked feed stock by catalytic hydrocracking



June 2, 1964 H. F. MASON ETAL 3,135,682

PROCESS FOR PRODUCING GASOLINE FROM A CRACKED FEED STOCK BY CATALYTIC HYDROCRACKING Filed Jan. :5. 1961 .N Mme .r s 5 M Y R A E o ww N m as R E D MM w RHM A 40v. HJL

Y. B k 2 w? 2 2 5 m ud V m W a Q H S j m d o 3 N m mzom m wzom N w w w 023655 u m 4 022056 A mw -zockNuzofl r m a S 25 220 9 m- N a .8 N NW A 2 A ow u t O N N N 3 3 3 K I M 3 2 wz3ow o m M21520 n um w R. d E x j H 1 96 2 0 United States Patent Oflice PRGCESS F612 PZRGDUCING GASGLM FRGM A CRAKED i lllll) STOCK BY CATALYTEQ HY- DRGQRACKING Harold F. Mason, Berkeley, John W. Scott, 3n, Ross, and Lyman S. Staten, Boron, Califi, assignors to California Research Corporation, San Francisco, Caliil, a corporation of Delaware Filed Jan. 3, 1961, Ser. No. 80,496 12 Claims. ((Jl. 208-68) This invention relates to a catalytic process for producing high quality gasoline from comparatively highboiling hydrocarbon fractions, and it is particularly directed to an integrated process involving a novel sequence of operating steps for producing high octane gasoline from petroleum stocks having an initial boiling point above about 325 F. and an end point below about 900 F.

This application is a continuation-in-part of our copending application Serial No. 575,254, filed March 30, 1956, now abandoned.

ISOMERIZATlON-CRACKING STEP The process of the present invention includes an isomerization-crackhig step wherein a hydrocarbon stock having an initial boiling point above about 325 F. and an end point below about 900 F. is contacted in an isomerization-craclring zone, in the presence of from about 1,500 to 30,000 s.c.f. H per barrel of total feed to said zone, with a catalyst composite comprising a hydrogenating-dehydrogenating component and an active cracking support. This contacting step is conducted at a temperature of from about 400 to 900 F., a pressure of at least 500 p.s.i.g., and an LHSV of from about 0.2 to 15. The etfiuentfrom the isomerization-cracking zone is then preferably freed of a hydrogen-rich recycle stream which is returned, along with make-up hydrogen to replace that consumed in the reaction, to that zone. The remaining portion of the efiluent is then separated so as to recover a gas fraction, at least one gasoline fraction, an intermediate fraction boiling above the heaviest gasoline fraction, having an initial boiling point of about 375i50 F., and an end point of about 475i25 F., and a bottoms fraction boiling above said intermediate fraction. A portion, and preferably all, of the intermediate fraction recovered from the isomerizanon-cracking zone is returned to that zone.

CATALYTIC CRACKING STEP The present invention is directed to the conversion of gasoline of straight-run, thermally cracked and, prefer- I ably, catalytically cracked, hydrocarbon fractions having initial T.B.P.s (true boiling point) of above about 325 F. and end points of below about 900 F. Among the fractions falling within this general range will be found those hydrocarbons which are known in the refin ing art as naphthas, gas oils, coker distillates, and cracked (thermally or catalytically) cycle oils. In any case, the feed, along with from about 1,500 to 30,000, and preferably fiom about 3,000 to 15,000 s.c.f. (standard cubic feet) of hydrogen per barrel of total reaction feed, is

passed into the isomerization-cracking zone at an LHSV (liquid hourly space velocity) of from about 0.2 to 15, and preferably from about 0.4 to 3.0, and intimately contacted with the catalyst.

NITROGEN CONTENT OF FEED While the invention can be practiced with utility in connection with petroleum feeds to the isomerization-cracking zone containing relatively large quantities of nitrogen, the operation becomes much more economical with stocks containing less than 200 p.p.m., preferably below ppm, and much more preferably below 10 ppm, of nitrogen. A reduction in feed nitrogen level permits the isomerization-cracking reaction to be conducted at lower temperatures than with feeds containing relatively large amounts of nitrogen compounds. Therefore, in the case of feed stocks which are not inherently low in nitrogen, acceptable levels can be reached by pretreating the feed to the catalytic cracking unit by a nitrogen compound extraction process, or by contacting either the catalytic cracking unit feed or, preferably, the particular feed to the isomerization-cracking process with hydrogen in the presence of a suitable catalyst at elevated temperatures and pressures to remove nitrogen compounds therefrom. A particularly efiective catalyst for removing nitrogen by hydrogenation is one wherein a co-precipitated molybdena-alumina material (e.g., one prepared in accordance with the disclosure of US. Patent No. 2,432,286 to Claussen et al., or US. Patent No. 2,697,006 to Sieg) is combined with cobalt oxide, the final catalyst having a metals content equivalent to about 2% cobalt and 7% molybdenum. Representative processing conditions for removing nitrogen with this catalyst are an LHSV of 1-3, 700-800 F., 2004500 p.s.i.g., and 1000l5,000 s.c.f. H per barrel of feed stock.

OPERATING CONDITIONS The contacting step is conducted under a pressure of at least 500 p.s.i.g., and preferably from about 800 to 3,000 p.s.i.g. The temperature is maintained in the range of from about 400 to 900 F., preferably from about 500 to 800 F., because, at temperatures above about 800 F, the amount of gasoline product lost to the less desirable C and lighter materials rapidly increases, thus lowering the motor fuel yield. For example, it has been found that the amount of methane produced at 800 F.

er unit of converted product is approximately sixteen times as great as that formed at 700 F., and four times as great as that produced at 750 F. At higher temperatures the situation becomes much worse. Accordingl' resort is normally had to temperatures above about 750 F. only in the last stages of the catalyst on-stream period when it is desired to maintain relatively high activity at the expense of higher light gas losses or, in the case when the relatively high nitrogen-containing feeds are processed. Further, operations at temperatures above about 750 F. and at low or moderate pressures induce I a relatively rapid decrease in the activity of the catalyst as reflected by reduced per-pass conversion levels. Thus, when operating at 875 F. and at a relatively low pressure, for example 1500 p.s.i.g., on'a hydrofined light cycle oil feed, regeneration of a cobalt-molybdenum on silica aluminum catalyst is required in most instances after onstream periods of one day or less, which contrasts with on-stream periods of 100 to 300 or more hours at good activity as temperatures are maintained below about 825 F. With operation at 800 F. and higher with the same and similar feeds, but with nickel sulfide on silica-alumina, regeneration is required after on-stream periods of a few hundred hours or less, compared withoperation below 700 F, with which can be obtained on-stream pcriods of several thous md hours without regeneration. In

Patented June 2, 1964 composites, and the like, clays and similar materials.

g from anyone or more of entire catalysts v fuel uses as diesel'fuels, jet

the present process, it is recommended that the reaction be conducted at an initial on-streamtemperature from about 550 to 650 F, with a progressive increase to about 750 to 850 F., so as to maintain catalyst activit at a controlled level. The initial and terminal temperatures will vary, with character of feed and catalyst, within the over-all range specified above.

CATALYST, GENERAL 'The catalyst employed in the isomerization-cracking zone is one wherein a material having hydrogenatingdehydrogenating activity is deposited or otherwise disposed on an active cracking catalyst support. The cracking component may comprise any one or more of such acidic materials as silica-alumina, silica-magnesia, silicaalumina-zirconia composites, alumina-boria, fluorided as Well" as various acid treated drogenating components of the catalyst can be selected the various groups V, VI, VII

and VIII metals, as Well as the oxides and sulfides thereof,

' alone or together with promoters or stabilizers that may have by themselves small catalytic effect, representative materials being the oxidesand sulfides of molybdenum, ,tungsten, vanadium, chromium, and the like, as Well as of metals such as iron, nickel, cobalt, -desired, more than one component can be present, and good results have been and platinum. If hydrogenating-dehydrogenating obtained with catalysts containing composites of two or more of the oxides of molybdenum, cobalt, chromium,

and zinc, and with mixtures of said oxides with fluorine.

The amount of the hydrogenating-dehydrogenating component present can be varied within relatively wide limits of from, about 0.5 to 30% based on the weight of the AROMATICSCQNTENTyOF FRACTION RECY CLED TO ISOME RIZATION-CRACKING STEP e The amount and nature of'the catalyst hydrogenatingdehydrogenating component and the catalyst support in Y a preferred embodiment of the process of the present invention should enable the resulting catalyst composite T to effect the productionin the isomerization-cracking zone at reactionconditions of a product such that the inter- V mediate boiling range fraction to be recycled in whole or in part asiaforesaid .will still have a relatively high aro- The hydrogenating-dehymatic content compared with the aromatic content of" the original feed. Where said intermediate boiling range fraction is relatively aromatic, it is an excellent recycle stock for the isomerization-cracking zone, and contrib- -utesto an increased production of the desired gasoline fraction. This is. somewhat unexpected; heretofore the emphasis has been on avoiding the production of an aromatics-rich fraction in said boiling range because it has 'been felt that fractions in said boiling range were best usablej directly as fuels and fuel blending stocks without recyclingthem. Therefore, aromatics-free. fractions in 1 said boiling range were sought,

because an aromaticsrich fraction'in said boiling range isundesirable for'such fuels, and blending stocks 650" F. block temperature.

and Where CATALYST CHARACTERTSTICS REQUIRED T ACHIEVE AROMATlCS-RICH RECYCLE FRAC- TION 7 (1) SF, as defined below, less than 2.0.

(2) A cracking activity index, or CAI, as defined belOW,'Of' at least 50, and an iso/normal C -C paraffin production iso normal activity index, or INAI, as defined below, of more than 1.

The severity factor, SF, is a measure of the balance between cracking reactions, including disproportionation,

and aromatics hydrogenation. It is determined by sub' jecting the catalyst to a standard test wherein a trimethyl benzene feedstock is passed over the catalyst at 2.0 LHSV, 1200 p.s.i.g., 9000 s.c.f./bbl. hydrogen rate, and

The severity factor is defined'in terms of the products produced under such con-' ditions, as follows:'

aron1atics hydrogenation index aromatic cracking index where aromatics hydrogenation index v ar omatics converted minus aromatics in synthetic product aromatics converted aromatics cracking index aromatics in syntheticproduct i p I aromatics in feedtA t can be shown that A; SF= l AD where this is a high value thecatalyst has a" high selectivity for aromatics saturation. Accordingly, the preferredcatalysts for use in the processof the present invention are those having thelower severity factors,

is and if their severity factors are low enough, i.e., less than 2.0, they will be satisfactory regardless oftheir crack1'ng activity indices, or CAI, and regardless of their 'siso/normalactivity index, or INAI.

therefor. Accordingly, heretofore a catalyst, for exam- 7 I ple, platinumron silica-alumina, has been used having extremely :high aromatics-saturation activity, which has resulted in the production of non-aromatic products in *saidboiling range rather than a recycle stock.

' In addition to the foregoing reason for previousavoid- The cracking'activity index,'CAI is the volume percentconversion of a light cycle oil feed converted bythe 1 catalyst to products boiling below feed initial boiling point at conditions of: 2.0 LHSV,,1200,p.s.i.g., 6500 s.c.f./bbl. gas rate, and temperature below 630 F o through operation.

The is0, n0rmal activity index, I NAI, is the iso/normal ratio of C, C paraffins produced with the catalyst when a normal decane feed is used, compared with the thermodynamic equilibrium iso/ normal ratio of C -C paraifins,

ance" of the production of aromatics-rich, stocks in said boiling range, it hasnot been appreciated heretofore just how, even. had they. been desired, aromatics-rich stocks in said boiling rangecould havebeen produced efficiently and with predictability in a hydroc'racking'process from i feeds such as those used in theprocess of 'the present {invention I i 1 vwhich latter ratio is multiplied by a factor 'which"pro duces a result of l'. The iso/normal ratio or C4-C paraflins actually produced over a given catalyst is m'ulti-.

plied by this same factor to obtain the INAI of the a catalyst.

1 Synthetic 'product is pnoduct boiling below initial boiling point. of feed. j I V EXEMPLARY CATALYSTS Exemplary catalysts having satisfactory characteristics as aforesaid include those containing: (a) about 1 to 12% molybdenum oxide, (17) a mixture offrom 1 to 12% molybdenum oxide and from 0.1 to cobalt oxide, (c) mixtures of from about 0.5 to 10% each of cobalt oxide and chromium oxide, (d) 0.l10% nickel, oxide or nickel sulfide, (e) 01-10% cobalt, cobalt oxide, or cobalt sulfide, (f) mixtures of from 0.1 to 10% each of nickel and cobalt, as metal, oxide or sulfide, in each case the said hydrogenerating-dehydrogenating component being deposited on an active cracking support, comprising silica-alumina beads having a silica content of about 70 to 99%, the metal content on the support being adjusted Within the aforesaid ranges as required by some preparative methods to obtain satisfactory SF values. Thus, the molybdenum oxide catalyst can be prepared readily by soaking the beads in a solution of ammonium molybdate, drying the catalyst for 24 hours at 220 F., and then calcining the dried material for 10 hours at 1000 F. If cobalt oxide is also to be present, the

calcined beads can then be similarly treated with a solution of a cobalt compound, whereupon the catalyst is again dried and calcined. Under favorable operating conditions the isomerization-cracking catalyst will maintain high activity over periods of 50 to 300 or more hours. The activity of the used catalyst can then be increased, if desired, by a conventional regeneration treatment involving burning off catalyst contaminants with an oxygen-containing gas.

TYPES OF OPERATION TO WHICH PROCESS IS ADAPTED ployed for the respective reaction and regeneration zones.

However, since in carrying out the process of this invention the catalyst retains its activity over long periods of time, it is normally preferable, from an economic standpoint, to employ the fixed catalyst bed method of operation or some modification thereof.

EXAMPLES Extensive experimental data covering variations in feed composition, catalysts, and operating variables have been utilized in the development of plant process designs incorporating the inventive features of the subject process. In the following case examples and detailed description of a preferred embodiment of the present invention, the operating variables and conversion factors have been determined by correlation of experimental data and projected for full-scale plant operations in accordance with the specific process design and feed composition. Thus, in the following cases examples, the results that can be expected from a 10,000 b.p.d. (barrels per day) isomerization-cracking zone under the specified operating conditions are shown in Table I. For comparative purposes only, case I shows an isomerization-cracking operation wherein the total bottoms fraction (i.e., that fraction boiling above the gasoline end point) and boiling in'the range of from about 400 to 570 F. is recycled to extinction. Case II shows an operation in accordance with the present invention, wherein only the portion of the bottoms fraction boiling from about 400 to 475 F. is recycled to extinction, with the remainder (boiling above about 475 F.) being withdrawn from the system.

Case I Case II Catalyst, 15% Molybdenum Oxide on Silica- .urnma. Fresh Feed, 400 to 570 F., Hydrofined Catalytisally Cracked Cycle Oil, b.p.d 66 Recycle, b.p.d 3,340 Total Feed (including recycle) b.p.d-- 10, 000 LHSV 2 2 Temperature, F;

Initial On-Stream 700 700 Final Orr-Stream. 825 S25 Pressure, p.s.i.g 1, 50 1,500 Hg, sci/b. of Total Fee 6,000 6, 000 Hz Consumption, s.c.f./b. of Total Feed 1,300 870 Products:

Gasoline, 05+, b.p.d 5,000 4, e40 F-l Clear 88 Fl+3 ml. TEL -97 Bil-98+ Diesel Fuel, b.p.d.. 0 2, 220 Cetane N0.-." 48

From the above summary it can be seen that the present invention (case 11) can be expected to produce gasoline of higher octane number than could be expected by merely recycling the total bottoms fraction to extinction. In the light of current estimates on the millions of dollars of capital investment required to raise presentday premium motor fuels one F-l octane unit, the high octane gasoline product of the present invention is an extremely advantageous result. Furthermore, it should be noted that the non-recycled portion of the isomerization-cracking unit bottoms (boiling above about 475 F.) can be expected to be an excellent diesel fuel of high cetane number.

PERATION WIIH CATALYTIC CRACKING 7 STEP, GENERAL As noted hereinbefore, a preferred embodiment of the present invention provides for the integration of a catalytic cracking unit with an isomerization-cracking process. On first considering the combination of these two specific units, it appeared that the catalytic cracking unit should act as the source of the preferred isomerization-cracking unit feed, namely, cracked cycle oil, and that operations should be conducted so as to recycle all of the portions of the efiuent boiling above about 325 F. from the isomerization-cracking zone either to that zone (extinction re cycle) or to the catalytic cracking unit for further cracking. However, it was discovered that if the process combination were operated according to the method outlined below, and shown in the appended drawing, considerable advantages could be expected over the possible recycle systems initially considered.

According to this preferred embodiment, a hydrocarbon fraction suitable for use as a feed stock to a catalytic cracking unit (such as, for example, a straight-run distillate in the nature of gas oil obtained from crude petroleum by simple distillation) is contacted in a cracking zone with an active cracking catalyst under conditions adequate to effect substantial cracking of the feed. The resulting efiiuent is passed into a separation zone from which is recovered. a gas fraction, a gasoline fraction, an intermediate fraction having an initial boiling point of about 375i50 E, and an end point of below about 900 F., and a heavy bottoms fraction. The intermediate fraction comprises the fresh feed to an isomerization-cracking unit of the type hereinbefore described. The conditions maintained in the latter unit are also the same as those previously described. The effluent from the isomerizationcracking zone is then freed of a hydrogen-rich recycle stream which is returned, along with make-up hydrogen to At least a portion, and preferably all, of the intermediate fraction recovered from the effluent of the isomeriza- I tion-cracking zone desirably is recycled to that zone, since itshigh aromatic content makes it very refractory to catalytic cracking. Furthermore, it has been found that, despite its refractory nature to catalytic cracking, thisintermediate fraction is readily converted in the isomerization-crackiug zone to high'octane gasoline boiling below the initial point of the recyclefraction.

Regardless of the amount of the intermediate fraction recovered from the isomerization-cracking zone that is recycled to that zone (as outlined above) it is desirable to recycle at least a portion of the heavy bottoms fraction (having an initial T.B. P. of about/$75 :25 F.) recovered from the isomerization-cracking zone efiluent to the cata- V V lytic cracking zone. It has been found that this fraction is less refractory in catalytic cracking than conventional light catalytic cycle oil and is morerefractory than such cycle stock in the isomerization-cracking reaction. Thus,

a preferred embodiment of the subject invention employs operating'variables and conversion factors that have been determined by correlation with experimental data and and a tar bottoms fraction;(amounting to about 500 b.p.d.) is recovered and passed from the system by line 34. By employing the noted stock as a feed to a-fluidtype cracking unit, employing a silica-alumina catalyst, a gasoline production and recovery of about'3,500 b.p.d. (based on about a 400 F. end point product) can be expected to be recovered from separation zone'11 by line 15.

The intermediate fraction. recovered'from separation .(or fractionation).zone 13, amounting to about 4,500 b.p.d., comprises a major proportion of the feed to theisomerization-cracking zone 19. This intermediate fraction is. supplied to the latter unit through line 16, along with a hydrogen-rich'gas stream supplied through line 20, the latter stream (which. includes both make-up hydrogen entering the system by line 21 as well as recycle hydrogen 1 from line 20) being supplied inan amount of from about 1,500 to 30,000, and "preferably. from about 3,000 to 15,000 s.c.f. (standard cubic feet) per barrel oftotal reactor feed, said feed including the intermediate fraction from catalytic cracking zone 11 entering by line 16 as Well as recycle through line 31 from isomerization-cracking zone 19, as hereafter described. Additional isomerization-cracking feed can be introduced into the system i from an external-source if desired. Forexample, light thermally cracked cycle oil from a refinery thermal crack- I ing unit can be passed into isomerization-cracking zone 19 projected for full-scale" plant operations in accordance with the specific process'design and feed composition. For comparative purposes only, the advantages ofthe ysubject process are demonstrated for processing an increment of light straight-run gas oil through a catalytic V. cracking unitin alargerefinery running mixed California crude oils, with a common light cycle oil stream from allv catalytic cracking in the refinery.

Referring to the figure of the appended drawing, which is a simplified flow scheme of. a refinery unit suitable for usein practicing-:the invention, 10,000b.p.d. (barrels per day) ofstraight-run light gasoilfeed. are passed byline 10 into catalytic crackingzonell wherein it is contacted,

; under cracking'conditions,.witha cracking catalyst. Al-

though the present description is concerned with the cracking of a particular gas oil fraction (light gas oil), the subject process can employ as the feedto thecatalytic cracking unit any hydrocarbon fraction that lendsitself to the catalytic cracking operation such'asheavy. gas oil, heavy hydrocarbons derived from oil shale or tar sands, or syn? theticfuel processes, andthe like. The catalytic crack- -ing reaction may be performed in any particular unit or processdirected to that end. For example, it may be done in any of the conventional processes. such as the fixed catalyst bed operation of the Houdry commercial units, .or" the Thermofor or 'fluid type moving catalystprocesses.

The efiiuent from catalytiocracking zone .11 is removed therefrom by line 12mm which it is passed into primary fractionation zone 13 wherein it undergoes separatien into various boiling range fractions As. shownin the drawing, a'normally'gaseous (C s,- C s, and lighter) fraction is recovered byline 14, a gasoline fraction having 'an initial T.B.P. of about 60F. and an end point of from about 325. to 425 l-E. is recovered as a product by line.

15,; an intermediate fraction having an initial T.B.P. of

aboyeabout 325 *P. (depending upon --the cut point of the gasoline) and an endpoint below'about' 650 F. is recovered froni, Zone 13' byline 16,:a bottomsfraction,"

boiling above said intermediate fraction and normally through lines 35, 31 and 16 for conversion to gasoline.

The present embodiment is based upon a total H of approximately 6,000 s.c.f. per barrel of total feed.

The isomerization-cracking. step is conducted as hereinbefore noted, i.e., a pressure of at least 500 p.s.i.g. and preferably from about 800 to 3000 p.s.i.g.; a temperature of between about 400 to 900 F., preferably 500 to 800 F.; an LHSV of from about 0.2 to 15, preferably about 0.4 to 3.0, and .a catalyst meeting the requirements discussed above. The presentprocess with feeds low in nitrogen (hydrofined) can beoperated to advantageat a' pressure of about 1500 p.s.i.g.; a space rate below about 2 LHSV; and aninitial oil-stream temperature of about 550 to 650 F., with progressive increase to about 750 to 850 F. With high-nitrogen feeds, similar conditions may be used, except'that the temperatures during the on-stream period may be about 5 0F. higher. As to the catalyst, the

presentdesign is based on data obtained with catalysts 7 having molybdenum oxide (1% byweight Mo) deposited on a synthetic silica-alumina gel cracking'support (con .tainingapproximately 87% silica and 13% alumina),,or

both cobalt oxide (2.3%,.Co) and molybdenum oxide (7.3% Mo), orcobalt 2.0% C0) and chromium (3.5%

Cr), supported by the same type or silica-alumina gel.

The total etfiuent fromthe isomerization-cracking. zone 19 is removed from that zone by line 22. Ifthefeed to 7 zone 19 is one which contains nitrogencompoundsithe reactor efiiuent will also contain ammonia due to the hy- I drogen'ationof the nitrogen compounds. These can be removedin the manner outlined in our copending application Serial No. 542,156. In any case, theeffiuent is p cooled and passed by line 22 into a high pressure-gasliquidseparator 23 from'which a'hydrogen-rich recycle stream is withdrawn overhead and returned, along with i make-up hydrogen entering by line 21, by line 20 to the isomerization-cracking zone. According to this particular preferably passed by line 24 int'o a" low pressure vapor- 1 liquid separator 25 to remove C and lighter normally design andfeed,'a' hydrogen consumption of about'l200 1 to 1600 act. per barrel of fresh isomerization-cracking unit feed (360-470 s.c. f ./bbl. based on the original; gas oil feedto the catalytic cracking zone,11) can beexpected,

thus requiring a corresponding amount of hydrogen to be added through line 21. The remainder of the efiiuentis gaseous components by line 26. The remaining normally termed Iheavy 'cycle oil, is" recovered by line :17 from I which it is preferably returned by lines 18 and 10 to the catalytic cracking zone 11 as a component of the feed,

liquid portion of the efliuent is then passed by line 27 into secondary fractionation zone 28 from which is' recovered a relatively light' gas fraction (C s and lighter) by lines 29 and 26, a gasoline fraction'(amounting to 3,000 b.'p.d.)

9 by line 30, an intermediate fraction (1500 b.p.d.) boiling in the range of from about 400 to 475 F. by line 31, and a bottoms fraction boiling above about 475 F., amounting to about 1500 b.p.d., by line 32.

Following the above-noted separation step, the intermediate iraction is recycled as a component of the feed to the isomerization-cracking zone 19 by lines 31 and 16 wherein it undergoes further conversion to gasoline. The bottoms fraction recovered from fractionation zone 28 by line 32 on be diverted from the system by line 33 and employed as an excellent diesel (cetane number generally above about 45), jet, turbine, or other fuel where a low aromatics content is desirable, or processed further as desired.

RESULTS OBTAINABLE WITH PROCESS OF PRESENT INVENTION With the particular design and feed stock described above, it can thus be expected to produce about 6500 b.p.d. (3500 b.p.d. from the catalytic cracking unit and 3000 b.p.d. from the isomerization-cracking unit) of gasoline of an octane number of around 96-100 F1+3 ml. TEL. Further, about 1500 b.p.d. of excellent diesel fuel can be expected, thereby giving a total of about 8000 b.p.d. of valuable gasoline and diesel fuel.

To atford a means of comparison, from available data a process design was developed to cover the same basic two-reaction system except that the total bottoms (about 400 F.+initia1 boiling point) from the isomerizationcracking zone is recycled to the isomerization-cracking zone Where it undergoes further reaction. Under such a scheme, a total gasoline production or" 8000 b.p.d. (from a 10,000 b.p.d. fresh catalytic cracking feed) with a hydrogen consumption of about 15001700 s.c.f. per barrel of fresh isomerization-cracking unit feed (650-700 s.c.f./bbl. of original gas oil feed to the catalytic cracking zone 11) can be expected. However, even though the gasoline output in this latter case may be slightly more than the process of the present invention, the subject invention provides for about a 33 percent decrease in isomerization-cracking zone size and about a 45 percent reduction in the amount of hydrogen (based on the original catalytic cracking unit feed) necessary for the isomerization-cracking reaction. Obviously, these reductions are of considerable economic importance to the refiner who must meet the present day gasoline requirements of high compression engines at the lowest possible cost.

When operating the present process with recycle to the isomerization-cracking zone of the intermediate fraction recovered therefrom, and also with recycle to catalytic cracking zone 11 through line 18 of the fraction boiling above this intermdiate fraction, the following advantageous results are obtained. When operations are conducted in this manner, a total of about 7600 b.p.d. (4100 barrels produced in the catalytic cracking unit and 3500 b.p.d. in the isomerlzation-cracking unit) of high octane gasoline (around 96l00 Fl+3 ml. TEL), with a hydrogen consumption of about 1200-1600 s.c.f. per barrel of fresh isomerization-cracking process feed (500- 670 s.c.f./bbl. based on original feed to the catalytic cracking unit 11), can be expected. Again, comparing these figures with the scheme wherein the total fraction from the isomerization-cracking unit boiling above gasoline is recycled to the catalytic cracking process, it can be seen that about a 21 percent reduction isomerizationcracking unit size and about a 22 percent reduction in hydrogen consumption (based on gas oil feed to the catalytic cracking unit) can be expected.

We claim:

1. A process for upgrading hydrocarbon stocks having an initial boiling point of above about 325 F. and an end point below about 900 F., which comprises contacting said stocks in an isomerization-cracking zone, in the presence of from about 1,500 to 30,000 s.c.f. H

per barrel of total feed to said zone, with a catalyst comprising a hydrogenating-dehydrogenating component selected from the group consisting of (a) about 1 to 12% molybdenum oxilde, (b) a mixture of from about 1 to 12% molybdeum oxide and from about 0.1 to 10% cobalt oxide, (0) mixtures of from about 0.5 to 10% each of cobalt oxide and chromium oxide, (at) about 0.1 to 10% nickel metal, (e) about 0.1 to 10% nickel oxide, (7) about 0.1 to 10% nickel sulfide, (g) about 0.1 to 10% cobalt metal, (h) about 0.1 to 10% cobalt oxide, (i) about 0.1 to 10% cobalt sulfide, (j) mixtures of from about 0.1 to 10% each of nickel metal and cobalt metal, (k) mixtures of from about 0.1 to 10% each of nickel oxide and cobalt oxide, and (I) mixtures of from about 0.1 to 10% each of nickel sulfide and cobalt sulfide, said catalyst further comprising an active cracking support comprising silica-altunina having a silica content of about 70 to 99% at a temperature of from about 400 to 900 F, a pressure of at least 500 p.s.i.g., and an LHSV of from about 0.2 to 15; recovering from the efiiuent of said isomerization-cracking zone at least one normally gaseous fraction, at least one gasoline fraction, an intermediate fraction having an initial boiling point of about 375i50 F. and an end point of about 475i25 F., and a bottoms fraction boiling above said intermediate fraction; returning to the isomerization-cracking zone at least a portion of said intermediate fraction; and passing to a catalytic cracking zone at least a portion of said bottoms fraction.

2. The process of claim 1, wherein the catalyst is characterized by a severity factor (SF) less than 2.0.

3. A process for upgrading hydrocarbon stocks having an initial boiling point of above about 325 F. and an end point below about 900 R, which comprises contacting said stocks in an isomerization-cracking zone, in the presenec of from about 1,500 to 30,000 s.c.f. H per barrel of total feed to said zone, with a catalyst comprising a hydrogenating-dehydrogenating component selected from the group consisting of (a) about 1 to 12% molybdenum oxide, (b) a mixture of from about 1 to 12% molybdenum oxide and from about 0.1 to 10% cobalt oxide, (c) mixtures of from about 0.5 to 10% each of cobalt oxide and chromium oxide, (:1) about 0.1 to 10% nickel metal, (e) about 0.1 to 10% nickel oxide, (f) about 0.1 to 10% nickel sulfide, (g) about 0.1 to 10% cobalt metal, (h) about 0.1 to 10% cobalt oxide, (1') about 0.1 to 10% cobalt sulfide, (j) mixtures of from about 0.1 to 10% each of nickel metal and cobalt metal, (k) mixtures of from about 0.1 to 10% each of nickel oxide and cobalt oxide, and (l) mixtures of from about 0.1 to 10% each or" nickel sulfide and cobalt sulfide, said catalyst further comprising an active cracking support comprising silica-alumina having a silica content of about 70 to 99% at a temperature of from about 500 to 800 F, a pressure of at least 500 p.s.i.g., and an Ll-lSV of from about 0.4 to 3.0; recovering from the effluent of said zone a hydrogen-rich, gaseous fraction, a remaining normally gaseous fraction, at least one gasoline fraction, an intermediate fraction having an initial boiling point aboveabout 325 F. and an end point of about 475 25 F., and a bottoms fiaction boiling above said intermediate fraction; returning to the isomerizatioucracking zone said hydrogen-rich fraction and at least a portion of said intermediate fraction; and passing to a catalytic cracking zone at least a portion of said bottoms fraction.

4. A process for producing gasoline from a hydrocarbon fraction suitable for use as a feed to a catalytic cracking process, which comprises contacting said fraction with an active cracking catalyst in a catalytic cracking zone under cracking conditions; recovering from the efiiuent of said cracking zone at least one gas fraction, at least one gasoline fraction, an intermediate fraction having an initial T.B.P. above about 325 F. and an end point below about 900 F., and at least one fraction ,mixture of from about 1 to 12%; V g

from about 0.1 to 10% cobalt oxide, mixtures of 7 boiling above said intermediate fraction; contacting said intermediate fraction in an isomerization-cracking zone,

in the presence of from about 1,500 to 30,000 s.c.f. H per barrel of total feed to said isomerization-cracking zone, With a catalyst comprising a hydrogenating-dehydrogenating component selected from the group consistingof (a) about 1 to 12% molybdenum oxide, (12) a mixture of from about 1 to 12% molybdeum oxide, and from about 0.1 to 10% cobalt oxide, (0) mixtures of from about 0.5 to each of cobalt oxide and chro- -rnium oxide, (d) about 0.1 to 10% nickel metal, (e)

about 0.1 to 10% nickel oxide, (7) about 0.1 to 10% nickel sulfide, (g) about 0.1 to 10% cobalt metal, .(h) about 0.1 to 10% cobalt oxide, (1') about 0.1 to 10% cobalt sulfide, (j) mixtures of from about 0.1 to 10% each of nickel metal and cobalt metal, (k) mixtures of from about 0.1 to 10% each of nickel oxide and cobalt oxide, and-(l) mixtures of from about'0.1 to 10% each of nickel sulfide and cobalt sulfide, said catalyst further comprising an active cracking support comprising silica-alumina having a silica content of about 70 to 99% at a temperature of from about 400 to 900 F., a pressure ofat least 500'p.s.i.g., and an LHSV of from about 0.4 to 3,0; recovering from the efiiuent of said isomerization-cracking zone at least one gas fraction, at least one gasoline fraction, an intermediate fraction having aninitial TBP. above about 325 F. and an end point of about 475i25 F., and a bottoms fraction boiling above said intermediate fraction; returning'to the isomerization-cracking zone at least a portion of the intermediate fraction recovered from the effluent therefrom; passing to the catalytic cracking zone at least' a portion of the bottoms fraction recovered from the efiluent therefrom.

5. The process of claim 4, wherein a hydrogen-rich,

normally gaseous fraction is recovered from the efiluent of. the isomerization-crackirig zone and is returned as recycle to that zone. 7 V

6. The process of claim 4,-Wherein the catalyst in the isomerization-crack'ng zone is characterized by, a severity factor (SF) below 2.0.

7. The process of claim 4, wherein a hydrocarbon iraction having an initial T .B.P. about about 325 F. and an end point below about 900 F., and obtained from athermal cracking unit, is additionallypassed into the isomerization-cracking zone.

' (g) about 0.1 to 10% cobalt metal, ([1) about 0.l to 10% cobalt oxide, (2') about 0.1 to 10% cobalt sulfide,

of from about 800 to 3,000 p.s.i.g.,

oxide, and (1) mixtures of from about 0.1 to 10% each of nickel sulfide and cobalt sulfide, said catalyst'further comprising an active cracking support comprising silicaalumina having a silica'content of about 70' to 99% at a temperature of from about 500 to 800 F., a pressure and an LHSV of from about 0.4 to 3.0; recovering from the eiiluent'of said isomerization-cracking zone a hydrogn-rich gaseous fraction, a remaining normally gaseous hydrocarbon traction, a gasoline fraction, an intermediate fraction' having an initial T.B.P. above about 325 F. and an end point below about 500 F., and a bottoms fraction boiling above said intermediate fraction; returning to the isomerization-cracking zone the hydrogen-rich fraction and at least a portion of and intermediate fraction 30,000 s.c.f. H per barrel of total feed to said zone,

with a catalyst comprising a hydrogenating-dehydrogenating component selected from the group consisting of (a) about 1 to 12% molybdenum oxide, (b) a mixture of from aboutl to 12% molybdenum oxide and from about 0.1 to 10% cobalt oxide, (0) mixtures of from about 0.5 to 10% each of cobalt. oxide and chromium oxide,

(at) about 0.1 to 10% nickel metal, (e) about 0.1 to,

10 nickel oxide, (f) about 0.1 to 10% nickel sulfide,

(j) mixtures of from about 0.1 to 10% each of nickel metal and cobalt metal, (k) mixtures of from about 0.1 to 10% each of nickel oxide and cobalt oxide, and

l) mitxures oi from about 0.1 to 10% each of nickel 8. A process for producing gasoline from a petroleum fraction suitable for use as a feed toa catalytic cracking process, which comprises contacting said'fraction with an active cracldng catalyst in a catalytic cracking zone under cracking conditions; recovering from the efiluent of said cracking zone a gas fraction, at least one gasoline fraction, an intermediate fraction having an initial T.B.P. above about 325'F.-and an end point below about 900 F., and at least :one heavy fraction boiling above said intermediate fraction; returning at least a portion of said 1 heavy fraction to the catalytic cracking Zone; contacting said intermediate fraction in an isomerization-crackmg zone, in the presence or" from about 3 ,000 to 15,000 s.c.f. H per barrel of total feed to said isomerization-cracking 'zone, witha catalyst comprising a hydrogenating-dehy drogenating component selected from the group consisting of (a) about 1 to 12% molybdenumoxide, (b) a V molybdenum oxide and from about 0.5 to 10 each of cobalt oxide and chromium oxide, (a?) about 0.1 .to 10% nickel metal, (2) about 0.1 to 10% nickel oxide, (1) about 0.1 to 10% nickel sulfide, g) about-0.l to 10% cobalt metal, (11) about 0.1'to-10% cobalt oxide, (i) about 0.1 to 10% cobalt sulfide, ('1') mixtures of from about 0.1 to 10% each of nickel metal and cobalt metal, (k) mixtures of from about 0.1 to 10% each of nickel oxide and cobalt sulfide and cobalt sulfide, said catalyst further comprising an active cracking support comprising silicaalumina having a silica content of about 70 to 99 at a temperature of from about 500 to 800 F., a pressure" of at least 500 p.s.i.g., and an Ll-ISV of' from 0.2 to '15;

. recovering from the efiuent of said zone a-hydrogen-rich gaseous fraction, a'remaining normally gaseousfraction,

at least one gasoline fraction, an intermediate fraction having an initial boiling point above about 325 F. and an end point below about 500 F, and a bottoms frac- 1 tion boiling above said intermediate fractionyreturning to tne isomerization-cracking Zone the hydrogen-rich fraction'and at least a portion of the intermediate fraction recovered therefrom; passing to a catalytic cracking zone at least .a portion of'said bottoms fraction recovered therefrom. V V

11. The process of claim l0,'wherein the feed' to the;

isomerization-cracking zone is a catalytically cracked stock.

12. The processor" clahn 10, wherein the' feed to the isomerization-cracking zone is a thermally crackedistock.

References Cited in the ille of this patent UNITED STATES PATENTS i 7 2,428,692 VoorhieS Oct. 7, 1947 2,559,285 Deuce ;f July3, 1951 2,799,626 Johnson et al. July 16,- 1957 2,885,346 Kearby et al. May 5, 1959 r 2,970,102 Gardner Ian. 31, 1961' 3,008,895

Hahsfo'rd et al. Nov. 14,1961" UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No, 3,185,682 J 2 19 Harold F0 Mason et alo It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 61 for "Of 'read to column l line 14, for "'charactertics" read -="-characteristicsline '18 for "150 normal" read iso/normal line 32 for "aromatic" read aromatics -5 line 641 for "iso normal" read iso/ normal column 5 line 8 for oxide or" read ----nickel oxide or line ll for "hydrog'enerating" read hydrogenating same column 5 line 62, for "cases" read case column 6 in the table, Case 11 line 4 thereof for '6 66" read 6,660 same table, Case I line 12 thereof for "1 50" read 1,500 g column 9 line 53 for intermdiate" read intermediate 5 column 10, line 4, for oxilde read oxide line 5 for molybdeum read molybdenum -*-5 same column 10, line 36 for 'presenec" read presence column 12, line 8, for "hydrogn read;--- hydrogen line 15 for "Of and intermediate read 01? the intermediate line 36 for '10 read 10% *3 column 12 line 43 for mitxures" read mixtures Signed and sealed this 10th day of November 196% (SEAL) Attest:

ERNEST W, SWTDER EDWARD J, BRENNER Attesting Officer Commissioner of Patents 

10. A PROCESS FOR PRODUCING GASOLINE FROM CRACKED PETROLEUM STOCKS HAVING INITIAL BOILIN G POINTS ABOVE ABOUT 325*F. AND END POINTS BELOW ABOUT 900*F., WHICH COMPRISES CONTACTING SAID STOCKS IN AN ISOMERIZATIONCRACKING ZONE, IN THE PRESENCE OF FROM ABOUT 1,500 TO 30,000 S.C.F. H2 PER BARREL OF TOTAL FEED TO SAID ZONE, WITH A CATALYST COMPRISING A HYDROGENATING-DEHYDROGENATING COMPONENT SELECTED FROM THE GROUP CONSISTING OF (A) ABOUT 1 TO 12% MOLYBDENUM OXIDE, (B) A MIXTURE OF FROM ABOUT 1 TO 12% MOLYBDENUM OXIDE AND FROM ABOUT 0.1 TO 10% COBALT OXIDE, (C) MIXTURES OF FROM ABOUT 0.5 TO 10% EACH OF COBALT OXIDE AND CHROMIUM OXIDE, (D) ABOUT 0.1 TO 10% NICKEL METAL, (E) ABOUT 0.1 TO 10 NICKEL OXIDE, (F) ABOUT 0.1 TO 10% NICKEL SULFIDE, (G) ABOUT 0.1 TO 10% COBALT METAL, (H) ABOUT 0.1 TO 10% COBALT OXIDE, (I) ABOUT 0.1 TO 10% COBALT SULFIDE, (J) MIXTURES OF FROM ABOUT 0.1 TO 10% EACH OF NICKEL METAL AND COBALE METAL, (K) MIXTURES OF FROM ABOUT 0.1 TO 10% EACH OF NICKEL OXIDE AND COBALT OXIDE, AND (L) MIXTURES OF FROM ABOUT 0.1 TO 10% EACH OF NICKEL SULFIDE AND COBALT SULFIDE, SAID CATALYST FURTHER COMPRISING AN ACTIVE CRACKING SUPPORT COMPRISING SILICAALUMINA HAVING A SILICA CONTENT OF ABOUT 7O TO 99% AT A TEMPERATURE OF FROM ABOUT 500* TO 800*F., A PRESSURE OF AT LEAST 500 P.S.I.G., AND AN LHSV OF FROM 0.2 TO 15; RECOVERING FROM THE EFFLUENT OF SAID ZONE A HYDROGEN-RICH GASEOUS FRACTION, A REMAINING NORMALLY GASEOUS FRACTION, AT LEAST ONE GASOLINE FRACTION, AN INTERMEDIATE FRACTION HAVING AN INITIAL BOILING POINT ABOVE ABOUT 325*F. AND AN END POINT BELOW ABOUT 500*F., AND A BOTTOMS FROCTION BOILING ABOVE SAID INTERMEDIATE FRACTION; RETURNING TO THE ISOMERIZATION-CRACKING ZONE THE HYDROGEN-RICH FRACTION AND AT LEAST A PORTION OF THE INTERMEDIATE FRACTION RECOVERED THEREFROM; PASSING TO A CATALYTIC CRACKING ZONE AT LEAST A PORTION OF SAID BOTTOMS FRACTION RECOVERED THEREFROM. 